1. Field of the Invention
The present invention relates in general to an automated control system for a power distribution switch, and in particular to a sensing mechanism for determining switch position.
2. Description of Related Art
Several power utility companies have recently employed automated power grid networks to redistribute or reroute electricity throughout service areas. These power companies reroute electrical power via power distribution switches located throughout a city or a community. Remotely controlled actuators, which are attached to the switches, selectively throw the switches to reroute the power.
These switches are a key part of the power grid as they allow for the rerouting of power around problem areas. The actuation of these switches, when called upon, is very critical. Blackouts and brownouts can occur if the automated system does not operate properly.
An actuator and its enclosure are normally mounted on the top or side of the power distribution switch. A shaft of the actuator is coupled to a lever of the distribution switch. Movement of the actuator shaft moves the lever to throw the switch.
The actuator shaft and the coupled lever commonly reciprocate between an open position and a closed position. In the open position the switch establishes a first power routing condition, and in the closed position the switch establishes a second power routing condition.
A central control system controls the switches of the power grid, and hence, controls the distribution of power throughout the associated service area. The central control system communicates with remote terminal units, each of which directly controls several switch actuators. The remote terminal unit selectively powers a specific switch actuator when instructed to do so by the central control system.
Limit switches communicate with the remote terminal unit to control the extent of actuator travel. Specifically, the limit switches establish "stops" (i.e., the point at which the actuator's travel stops).
Prior limit switches have been used in conjunction with triggering mechanisms which trip the limit switches at predefined points along the length of the actuator travel. Such trigger mechanisms generally have been adjustable so that the points at which the mechanism trips the corresponding limit switches can be varied along the length of the actuator travel. The triggering mechanism thus allows for the stops of the actuator to be adjusted to define specific stroke lengths of the actuator.
When the central control system signals a particular remote terminal unit to switch a specific power distribution switch, the remote terminal unit connects an electric motor of the actuator to a source of power. The electric motor drives the actuator shaft in the desired direction to move the lever and throw the switch to establish a desired power routing condition. At the position where the actuator throws the switch, the triggering mechanism attached to the actuator trips the limit switch, which in turn communicates with a power supply of the remote terminal unit to stop the actuation of the switch actuator.